Time Vault

Time Vault enters tapped.
Time Vault doesn't untap during your untap step.
If you would begin your turn while Time Vault is tapped, you may skip that turn instead. If you do, untap Time Vault.
{T}: Take an extra turn after this one.

Garth One-Eye

{T}: Choose a card name that hasn't been chosen from among Disenchant, Braingeyser, Terror, Shivan Dragon, Regrowth, and Black Lotus. Create a copy of the card with the chosen name. You may cast the copy. (You still pay its costs.)

Prophet of Kruphix

Untap all creatures and lands you control during each other player's untap step.
You may cast creature spells as though they had flash.

Rofellos, Llanowar Emissary

{T}: Add {G} for each Forest you control.

Tolarian Academy

{T}: Add {U} for each artifact you control.

Yawgmoth's Bargain

Skip your draw step.
Pay 1 life: Draw a card.

Recurring Nightmare

Sacrifice a creature, Return Recurring Nightmare to its owner's hand: Return target creature card from your graveyard to the battlefield. Activate only as a sorcery.

Library of Alexandria

{T}: Add {C}.
{T}: Draw a card. Activate only if you have exactly seven cards in hand.